Understanding the charge-separation mechanism in organic photovoltaic cells (OPVs) could facilitate optimization of their overall efficiency. Here we report the time dependence of the separation of photogenerated electron hole pairs across the donor-acceptor heterojunction in OPV model systems. By tracking the modulation of the optical absorption due to the electric field generated between the charges, we measure ~200 millielectron volts of electrostatic energy arising from electron-hole separation within 40 femtoseconds of excitation, corresponding to a charge separation distance of at least 4 nanometers. At this separation, the residual Coulomb attraction between charges is at or below thermal energies, so that electron and hole separate freely. This early time behavior is consistent with charge separation through access to delocalized π-electron states in ordered regions of the fullerene acceptor material.

The successful development of a photocatalyst/biocatalyst integrated system that carries out selective methanol production from CO2 is reported herein. The fine-tuned system was derived from a judicious combination of graphene-based visible light active photocatalyst (CCG-IP) and sequentially coupled enzymes. The covalent attachment of isatin-porphyrin (IP) chromophore to chemically converted graphene (CCG) afforded newly developed CCG-IP photocatalyst for this research endeavor. The current work represents a new benchmark for carrying out highly selective methanol formation from CO2 in an environmentally benign manner.

The successful development of a triazine based covalent organic framework as an inexpensive and highly efficient visible light active flexible film photocatalyst for solar fuel production from CO2is described.

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The utilization of CO 2 for production of solar fuels/chemicals is gaining increasing importance due to worldwide fossil-fuel shortage and global warming. As a means to achieve this, we herein report on the synthesis and development of a graphene-based visible light active photocatalyst (CCG-BODIPY) which is chemically converted graphene (CCG) covalently bonded to a light harvesting BODIPY molecule (1picolylamine-2-aminophenyl-3-oxy-phenyl-4,4 0 -difluoro-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4adiaza-s-indacene-triazine). The photocatalyst-biocatalyst coupled system developed using CCG-BODIPY as photocatalyst functions in a highly efficient manner, leading to high NADH regeneration (54.02 AE 0.61%), followed by its consumption in exclusive formic acid production (144.2 AE 1.8 mmol) from CO 2 . The present research endeavour highlights the development and application of a graphene based photocatalyst for direct solar fuel formation from carbon dioxide.

Covalent organic frameworks (COFs) have emerged as a promising light-harvesting module for artificial photosynthesis and photovoltaics. For efficient generation of free charge carriers, the donor–acceptor (D-A) conjugation has been adopted for two-dimensional (2D) COFs recently. In the 2D D-A COFs, photoexcitation would generate a polaron pair, which is a precursor to free charge carriers and has lower binding energy than an exciton. Although the character of the primary excitation species is a key factor in determining optoelectronic properties of a material, excited-state dynamics leading to the creation of a polaron pair have not been investigated yet. Here, we investigate the dynamics of photogenerated charge carriers in 2D D-A COFs by combining femtosecond optical spectroscopy and non-adiabatic molecular dynamics simulation. From this investigation, we elucidate that the polaron pair is formed through ultrafast intra-layer hole transfer coupled with coherent vibrations of the 2D lattice, suggesting a mechanism of phonon-assisted charge transfer.

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